Locking system for tilting firearm bolt



Dec. 3, 1963 R. H. COLBY LOCKING SYSTEM FOR TILTING FIREARM BOLT Filed June 22, 1962 3 Sheets-Sheet 1 H IT P MN INVENTOR. Rich; Hljulh BY 1 1.12%: QJS M T mg: h ww -H Dec. 3, 1963 R. H. COLBY 3,112,675

LOCKING SYSTEM FOR TILTING FIREARM BOLT Q Filed June 22, 1962 3 $heets-Sheet 2 W 0N Y R IV 5 c9 wm 3 M T y w 2Q Nw 1m 1 v 8 ix H \liiiiuil Dec. 3, 1963 R. H. COLBY LOCKING SYSTEM FOR TILTING FIREARM BOLT 3 Sheets-Sheet 3 Filed June 22, 1962 INVENTOR fil'c huri H. Bulky United States Patent '0 The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to automatic firearms of the machine gun class and more particularly to the bolt mechanisms therefor.

The systems for locking-reciprocating firearm bolts in battery generally fall into two categories. In one, the bolt is provided at the front end with locking abutments which are rotatable into locking engagement with cooperating locking abutment-s in the firearm receiver or barrel extension. This system is distinguished for its strength and rigidity because of the proximity of the locking abutments on the bolt to the breech of the barrel but the rotary. locking requires cam actuation that effects considerable frictional losses.

In the other system, the rear end of the bolt is tilted or displaced sideways to engage locking abutments on the bolt with cooperating abutments in the receiver. This system has the advantage of requiring very little energy for the locking sequence but it is not as rigid as that of the rotary class because .of the distance between the locking areas and the breech end of the barrel which permits deflection of the bolt or receiver structure therebetween.

It is, therefore, an object .of this invention to provide for firearms having a reciprocating bolt a locking system having the rigidity and strength of the rotary locking system and the low frictional losses of the tilting bolt.

It is another object of this invention to provide a bolt mechanism in which the bolt is pivoted around a fulcrum at the rear end and locking engagement is made with the receiver adjacent the'breech end of the barrel.

-It is a further object of this invention to provide a bolt mechanism having a carrier and a bolt pivot-ally mounted at the rear end thereof to the rear end of the carrier to provide a compact device, with a firing pin mounted to the carrier for pivotal displacement with the bolt so as to be out of alignment with the primer of the chambered cartridge until the bolt is secured in locked position.

It is still another object of this invention to provide a bolt mechanism which is simple and rugged in design and positive in operation.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

FIG. 1 is a longitudinally cross-sectioned view of the receiver section of a rifle showing the bolt in locked battery position;

FIG. 1a is a partially cross-sectioned view of the section of the rifle forwardly of that shown in FIG. 1;

FIG. 2 is a fragmentary view similar to FIG. 1 but showing the bolt carrier in the recoil position;

FIG. '3 is a view taken along line '3--3 of FIG. 1;

FIG. 4 is a view taken along line 4-4- of FIG. 3;

FIG. 5 is a view similar to FIG. 4 but showing the relationship of the locking lugs in the receiver with the Patented Dec. .3, 1963 cooperating ribs on the bolt head when the bolt .is adjacent the locked position; and

FIG. 6 is an exploded, perspective viewof the carrierbolt group.

Shown in the figures is a machine gun 12 having a receiver 14 with a barrel 16 extending forwardly therefrom. Agas cylinder 18 is mounted underneath barrel 16 with the rear end received by the front end of receiver 14. A gas port 20 provides means for bleeding discharge gases from barrel 16- into gas cylinder 18 approximately midway the length thereof to establish a gas expansion chamber .22 forwardly of the gas port. Slidingly mounted in gas cylinder 18 is a piston 24 which is attached at the rear end to a carrier 26 mounted in receiver 14-, as hereinafter described, for longitudinal displacement between a battery and a recoil position.

Carrier 26 includes a rectangular base 28 which is connected at the front end to piston 24 by ball and socket means 30. A rib 3 2. extends longitudinally along each side of base 28 and is slidingly received by a cooperating longitudinally disposed channel 34 formed along the adjacent inner Wall of receiver 14 for guiding carrier 26 in its reciprocation. Extending vertically upward from base 28 at the rear section-thereof is a flange 36 which extends longitudinally along the base symmetrical to the sides thereof.

Carrier 26 mounts a bolt 38, as hereinafter described, for relative longitudinal and pivotal displacement. Bolt 38 includes a head 46* for closing the breech of barrel 16 after a cartridge 42 is chambered therein. Arammer 44 projects upwardly from head 40 for transferring cartridge 42 from a feeding mechanism (not shown) into the chamber-of barrel 16 and an extractor -to be more fully described hereinafter, is slidingly disposed in a T-slot 48 vertically formed in the front. face of the head.

A pair of laterally spaced arms 50" extend rearwardly from head 40 to straddle flange .36. The-ohannelformed between arms 50 is terminated at the front 'end' by a wall 52 of inverted steplike configuration whichincludes-a vertically formed upper wall 54 and. a vertically formed lower wall 56 spaced forwardly and below the upper wall. Flange 36 is terminated at the front end by a front face 58 which hasa configuration the exactreverse of that of wall 54 and which is arranged to "be :matingly contactable therewith. A firing pin 60 is pivotally mounted on flange 36 so as to extend. forwardly from front face 58 and be slidingly received by .a mating bore 6'2 which extends through head 4% from upper wall 54'. Firing pin 60 is arranged so that the strikerend thereof extends forwardly from head 40 when wall '52 and front face 58 are in contact.

Formed transversely through flange as at the rear section thereof is a longitudinally elongated slot 63 which is closed at both ends. A pin 64 extends laterally through arms 50 adjacent the rear ends thereof and is slidingly received by slot 63 so as to provide a fulcrum for the pivotal displacement of bolt 38 between a "lower unlocked position and an upper locked position, relative to carrier 26, while permitting relative longitudinal displacement of the bolt and carrier between a firing position wherein wall 52 and front face 58 are in contact and a pickup position at which rearward displacement of carrier 26 is transferred to bolt '38 during actuation of the carrier to the recoil position.

This rearward pickup of bolt 33 by carrier 26 is achieved through the cooperation of a pair of bosses 65 formed on opposite sides of flange 36 with a pair of clearances 66 formed in the undersides of the arms '50. The bosses '65 respectively include a rear face 67 which is conta'ctable with a rear end 68 on each of the clear- 3 ances 66 when carrier 26 is displaced rearwardly relative to bolt 3-8 to the pickup position.

The pivotal displacement of bolt 38 is effected through the cooperation of a cam slot 69 formed in the forward section of flange 36 with a pin 76 which is mounted between arms 50 therein so as to extend through the cam slot. Cam slot 69 includes a longitudinal section '74 and an arcuate section 76 which continues forwardly and downwardly therefrom. Arcu ate section 76 includes a top cam surface 78 and a bottom cam surface 8%.

The length of pin 70 is greater than the width of carrier 26 so that the ends of the pin, noted at 82, extend from opposite sides thereof and such ends are received by channels 84 formed in the inner walls of receiver 14. Channels 84 extend longitudinally along the walls of receiver 14 sothat the ends 82 are slidingly engaged by the channels during displacement of carrier 24 between the battery and recoil positions. Channels 84 are positioned vertically so that, when ends 82 are engaged therewith, pin 70 is held in arcuate section 76, where the forward displacement of carrier 26 is transferred to bolt 36 through the contact of the pin with top cam surface 73. The rearward displacement of the carrier is transferred to the bolt by contact of the pin 76 with bottom cam surface 80 and bolt 38 is also held thereby in the unlocked position.

Provided at the front end of each of the channels 84 is a vertical extension 86 which permits upward displacement of pin 70 when ends 82 are in registry therewith which occurs when bolt 38 has chambered cartridge 42 in barrel 16. Thus, pin 70 is freed for upward displacement along arcuate section 76 by the camming action of bottom cam surface 80 with the pin and, as the pin is fixedly mounted to arms 56, the upward displacement of the pin raises bolt 38 to the locked position.

When in the locked position, bolt 38 is prevented from being displaced rearwardly relative to receiver 14 through the cooperation of a pair of vertically spaced ribs 88, formed on each side of head 40, with a pair of vertically spaced locking lugs 90 formed on each of the inside walls of receiver 14. Ribs 88 and locking lugs 90* are rectangular in cross-section and are elongated longitudinally and they all have the same vertical thickness. Ribs 88 and locking lugs 90 are so interrelated that, as bolt 38 nears the cartridge chambered position during forward displacement =of carrier 26, the top ones of the ribs 88 pass between the locking lugs 99 with the bottom ones thereof passing simultaneously between the ribs. When bolt 38 reaches the cartridge chambered position and ends 82 of pin 70 are in registry with vertical extensions 86, the rear ends of the ribs 88 are just free of the front ends of the locking lugs 96 so that, when bolt 38 is displaced upwardly, the ribs move in [front of the locking lugs to block rearward displacement of the bolt. At the same time, firing pin 60 is pivoted upwardly into alignment with the primer of the chambered cartridge 42.

Bottom :cam surface 89 and top cam surface 78 are each generated to displace head 40 a distance equal to the vertical thickness of ribs 88 and locking lugs 96 when pin 70 is displaced between arcuate section 76 and longitudinal section 74. After bolt 38 reaches the locked position with pin 70 positioned at the front end of longitudinal section 74, carrier 26 is free to proceed uninterrupted to the firing position so that the striker end of firing pin 60 strikes the primer of the chambered cartridge for discharge thereof. During this relative displacement of carrier 26 to the firing position, pin 70 is displaced along longitudinal section 74 to hold bolt 38 in the locked position.

Extractor 46 is conventionally provided at the bottom end thereof with an upwardly projecting claw 94 for engaging the extractor groove of cartridge 42 when chambered in barrel l6 and is biased upwardly to maintain the engagement by means of an extractor lifter 96 which is pivotally mounted on base 23 forwardly of flange 36.

Extractor lifter 96 is pivotaily mounted by means of a shaft 93 which extends laterally through the rear end of the extractor lifter and base 28 and is biased upwardly by a spring 169. Provided along the top of extractor lifter 96 is a fiat surface 162 which has sliding contact with the bottom of extractor 46 to transfer the bias of spring 160 to the extractor. Extractor lifter 96 is arranged so that flat surface 162 is in contact with extractor 46 during relative displacement of bolt 33 and carrier 26.

Provided between carrier 26 and the rear end of receiver M is a coiled compression spring 104 for biasing the carrier forwardly to the battery position and a buffer mechanism 166 is provided in the rear end of the receiver for absorbing the surplus recoil energy in the carrier. A trigger actuated sear mechanism 108 releasably holds carrier 26 in a seared position adjacent the recoil position.

When carrier 26 is scared up by sear mechanism 108, pin 76 is held in arcuate section 76 of cam slot 69 by the engagement of ends 82 with the channels 84 to hold head 46 down in the unlocked position. Upon actuation of scar mechanism 1%, carrier 26 is propelled forwardly through the bias of spring 164 with rammer 44 transferring a cartridge 42 from the feeding mechanism (not shown) into the chamber of barrel 16. When bolt 38 reaches the chambered position so that cartridge 42 is completely chambered in barrel l6, ends 82 are in registry with vertical extensions 86. This releases pin 70 for upward displacement by the camming action of bottom cam surface 84? therewith, therefore, bolt 38 is pivoted upwardly thereby to the locked position. As head 40 moves upwardly, firing pin 6 is pivoted upwardly therewith so as to be in alignment with the primer of the chambered cartridge 42 when bolt 38 reaches the locked position.

Bolt 38 is maintained in the locked position through the engagement of pin 76 with longitudinal section 74 of cam slot 69 and, with the entry of ends 82 thereinto, carrier 26 is free to proceed uninterrupted to the firing position wherein firing pin 64 strikes the primer of the chambered cartridge 42 for discharge thereof.

When the projectile of the discharge cartridge 42 passes gas port 26, the compressed gases pass through the gas port and enter chamber 22 to energize piston 24 for displacement to the recoil position. The energized piston 24 displaces carrier 26 rearwardly moving pin 76 along longitudinal section 74- of cam slot 69. When pin 79 enters arcu ate section 76, bolt 33 is actuated upwardly to the unlocked position so that ribs 88 are displaced free of locking lugs 90 and are positioned to pass rearwardly therebetween when rear faces 67 on the bosses 65 contact rear ends 68 of the clearances 66 at the pickup position of carrier 26 relative to bolt 38.

When rear faces 67 contact rear ends 68, bolt 38 is picked up by carrier 26 and is displaced rearwardly thereby. With extractor 46 having engagement with the spent case of cartridge 42, the spent ease is extracted from the chamber of barrel 16, as bolt 38 is displaced rearwardly, for eventual ejection from receiver 14. Carrier 26 with bolt 38 continues rearwardly, compressing spring and, when adjacent the recoil position, the surplus energy in the carrier is absorbed by buffer mechanism 196.

From the foregoing, it is clearly apparent that there is provided herein a bolt mechanism having a locking system that provides the rigidity and strength of the rotary type and which has the advantage of the tilting bolt system by requiring very little energy for actuation with the bolt mechanism also being distinguished for its compact structure and the pivotal mounting of the firing pin which is out of aligmnent with the primer of the chambered cartridge until the bolt is in the unlocked position and safe for discharge of the cartridge.

Although a particular embodiment of the invention has been described in detail herein, it is evident that many variations may be devised within the spirit and scope thereof and the following claims are intended to include such variations.

1 claim:

1. A firearm including a receiver, a barrel mounted in said receiver for (forward extension therefrom and adapted for receiving a cartridge in the breech end for discharge, a carrier mounted in said receiver for longitudinal displacement between a battery and a recoil position, a bolt adapted for transferring a cartridge from a feeding mechanism into said barrel and closing the breech end thereof, means for mounting said bolt at the rear end thereof to the rear end of said carrier for relative longitudinal and pivotal displacement, cam means operationally disposed between said carrier and said bolt at the front end thereof for effecting pivotal displacement of said bolt between a locked and an unlocked position responsive to longitudinal movement of said carrier relative thereto, and cooperating means on said bolt and in said receiver for preventing rearward displacement of said bolt when in the locked position.

2. The fireanm as defined in claim 1 and including a 6 firing pin pivotally mounted to said carrier for extension through said bolt so as to be out of alignment with the cartridge in said barrel when said bolt is in the unlocked position.

3. The firearm as defined in claim 1 wherein said cooperating means on said bolt and in said receiver include a pair or longitudinally elongated ribs formed on each side of said bolt at the front end thereof and a pair of locking lugs formed inside of said receiver adjacent the breech end of said barrel, said ribs being arranged to pass between said locking lugs when said bolt is in the unlocked position, and wherein said cam means are arranged to pivot said bolt upwandly when said ribs are just clear of said locking lugs and position said ribs in front thereof when said bolt is in the locked position.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A FIREARM INCLUDING A RECEIVER, A BARREL MOUNTED IN SAID RECEIVER FOR FORWARD EXTENSION THEREFROM AND ADAPTED FOR RECEIVING A CARTRIDGE IN THE BREECH END FOR DISCHARGE, A CARRIER MOUNTED IN SAID RECEIVER FOR LONGITUDINAL DISPLACEMENT BETWEEN A BATTERY AND A RECOIL POSITION, A BOLT ADAPTED FOR TRANSFERRING A CARTRIDGE FROM A FEEDING MECHANISM INTO SAID BARREL AND CLOSING THE BREECH END THEREOF, MEANS FOR MOUNTING SAID BOLT AT THE REAR END THEREOF TO THE REAR END OF SAID CARRIER FOR RELATIVE LONGITUDINAL AND PIVOTAL DISPLACEMENT, CAM MEANS OPERATIONALLY DISPOSED BETWEEN SAID CARRIER AND SAID BOLT AT THE FRONT END THEREOF FOR EFFECTING PIVOTAL DISPLACEMENT OF SAID BOLT BETWEEN A LOCKED AND AN UNLOCKED POSITION RESPONSIVE TO LONGITUDINAL MOVEMENT OF SAID CARRIER RELATIVE THERETO, AND COOPERATING MEANS ON SAID BOLT AND IN SAID RECEIVER FOR PREVENTING REARWARD DISPLACEMENT OF SAID BOLT WHEN IN THE LOCKED POSITION. 